1. Field of the Invention
The present invention relates to a fluid compressor and more particularly, to a helical blade type compressor for compressing refrigerant gas in a refrigeration cycle.
2. Description of the Related Art
It is known to use a helical blade type compressor for compressing fluids and/or gases. A compressor of this type is disclosed in U.S. Pat. No. 4,871,304 assigned to the present assignee. The compressor has a compression section driven by a motor and arranged in a closed case. The compression section is provided with a cylinder rotated together with a rotor in the motor. A piston having a center axis eccentric to the axis of the cylinder is rotatably housed in the cylinder. A spiral or helical groove is formed on the outer circumference of the piston in the axial direction thereof. The pitches of this spiral groove gradually narrow with the distance from one end of the piston to the other end. A blade having appropriate elasticity is fitted into the spiral groove.
The space between the cylinder and the piston is partitioned into a plurality of compression chambers by the blade. The volumes of the compression chambers gradually decrease with the distance from a suction side of the cylinder to a discharge side of the cylinder. When the cylinder and the piston are rotated in synchronization with each other by the motor, refrigerant gas in the refrigeration cycle in which the compressor is located is sucked into the compression chamber through the suction side of the cylinder. The gas thus sucked is successively fed to the compression chambers located on the discharge side of the cylinder while being compressed in the compression chambers. The compressed gas is then discharged into the closed case though the discharge end of the cylinder.
To increase the efficiency of the compressor without enlarging the size of the outer case, the diameter of the cylinder could be enlarged so that the volumes of the compression chambers are increased. As a result, more material can be compressed with each rotation of the rotor. However, increasing the diameter of the cylinder also requires increasing the diameter of the bearing members supporting the cylinder ends. As a result, the circumferential inner surface contact area at the right and left ends of the cylinder between the cylinder and bearing members is also increased. This increase in contacting surface area causes an increase in the friction between the cylinder and bearing members. A large drive force is thus needed to rotate the cylinder and piston to compensate for the increase in friction. Thus, smooth rotation of both the cylinder and the piston does not always occur due to the friction.